1. Field of the Invention
The present invention relates to a gas separation apparatus for separating specific gases from a mixture gas containing a plurality of gases.
2. Description of the Related Art
Conventionally, various gases are used in semiconductor manufacturing processes depending on the process. For example, perfluoro compound (PFC) gas which is a mixture containing fluorine compounds such as CF4, NF3, C2F6, C3F8, SF6, and CHF3 is used as a reaction gas at the dry etching process or at the thin film forming process. In these processes, discharge gas is produced which contains the PFC gas.
Because these discharge gases such as PFC cannot be discharged out of the manufacturing line as such, various methods are employed for treating these gases. The treating methods include (i) decomposition in which the PFC gas is decomposed by combustion, catalyst heating, or plasma decomposition; (ii) membrane separation in which these materials are separated by a membrane; and (iii) subzero cooling separation in which the separation is achieved taking advantage of the difference in the boiling points of the gases.
However, in the decomposition method (i), there are shortcomings in that a complete decomposition is difficult and the gas cannot be recovered for reuse because the gas is decomposed and discharged. In the membrane separation (ii), although nitrogen in the discharge gas can be removed, the separation between CF4 and NF3 or the like which have similar molecular size is difficult. In the above method (iii), the overall size of the apparatus becomes large, resulting in increased cost for the equipment and increased running cost. Moreover, because the boiling point difference between CF4 and NF3 is only 1xc2x0 C., the separation is difficult.
One object of the present invention is to provide a gas separation apparatus capable of separating a mixture gas having a plurality of gas constituents inexpensively and with high purity.
In order to achieve the object mentioned above, according to one aspect of the present invention, there is provided a gas separation apparatus for separating specific gases from a mixture gas to be treated containing the specific gases, the apparatus comprising: an adsorbing device for adsorbing the specific gases within the mixture gas to be treated by supplying the mixture gas to be treated and for desorbing the adsorbed specific gases by supplying a purge gas; and a separator for separating chromatographically the mixture gas containing the specific gases from the adsorbing device, into each of the plurality of gas constituents.
In this manner, by using a separator which performs chromatographic separation, separation of specific gases, such as, for example, CF4 and NF3, contained in the mixture gas to be treated, which are otherwise difficult to be separated, can be reliably achieved. The separated CF4 and NF3 can then be recovered and reused.
An adsorbing device is provided before the separator, in which device the specific gases are adsorbed and then desorbed by a purge gas. By adsorbing and then desorbing, the specific gases can be concentrated. In this manner, the specific gases, such as, for example, CF4 and NF3 can be reliably separated at the separator.
According to another aspect of the present invention, it is preferable that concentration means is further provided for independently concentrating the gas separated into each of the plurality of gas constituents and obtained at the chromatographic separator, and the concentrated gas obtained by the concentration means is recovered and reused.
A carrier gas (for example, nitrogen) is included in the specific gases separated chromatographically, such as, for example, CF4 and NF3. By removing the carrier gas by the concentration means, each of the specific gases can be recovered and reused.
According to another aspect of the present invention, it is preferable that a mixture gas containing the specific gases having a plurality of gas constituents is the PFC gas discharged from a semiconductor manufacturing process and the mixture gas to be treated contains nitrogen as another gas.
When the specific gases constitute the PFC gas, activated carbon or silica gel, or the like can be preferably used as the adsorbent. Also, for desorption, it is preferable to use nitrogen gas as the purge gas under an overheated condition.
According to another aspect of the present invention, it is preferable that the PFC gas contains one of fluorine compounds having at least one of the elements C, N, and S as a composition element.
According to another aspect of the present invention, it is preferable that the PFC gas includes one of CF4, NF3, C2F6, C3F8, SF6, or CHF3.
According to another aspect of the present invention, it is preferable that the above-mentioned concentration means is either a membrane separator which takes advantage of the permeability/impermeability of a membrane or a subzero cooling separator which takes advantage of difference in boiling points. With such a concentration means, concentration of the PFC gas, for example, can be effectively performed.
According to another aspect of the present invention, it is preferable that a plurality of chromatographic columns are provided and used in sequence. By using a plurality of columns, the separation process can be performed almost continuously.
According to another aspect of the present invention, it is preferable that the gases other than the specific gases separated at the separator contains nitrogen as the main constituent and the nitrogen gas is reused for a given usage.
According to another aspect of the present invention, it is preferable to perform a process to remove gas constituents other than the nitrogen gas on the gas containing nitrogen gas as its main constituent.